Actuating electromotor for technical devices, in particular in motor vehicles

ABSTRACT

The subject matter of the invention is an electric motor-driven servo-drive for use in technical means, especially motor vehicles, with a small electric drive motor ( 2 ) with a motor shaft ( 4 ) which is provided with a gear form-fit element ( 3 ) at at least one location, proceeding especially from the end, with a worm ( 5 ) of a worm gear pair, the worm ( 5 ) slipped onto the motor shaft ( 4 ), and with a worm wheel ( 6 ) of the worm gear pair, the wheel ( 6 ) consisting preferably of plastic and coupled to the worm ( 5 ) via teeth which engage one another. It is characterized in that the worm ( 5 ) consists of plastic, that a driver ( 7 ) consisting of a harder material which transfers higher torques than the plastic of the worm ( 5 ) is slipped onto the motor shaft ( 4 ) and with the corresponding shaft form-fit element engages the gear form-fit element ( 3 ) of the motor shaft ( 4 ), that the driver ( 7 ) on a diameter which is much greater than that of the motor shaft ( 4 ) has a worm form-fit element, and that the worm ( 5 ) for its part has a driver form-fit element which engages the worm form-fit element of the driver ( 7 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an electric motor-driven servo-drive for use intechnical means, especially motor vehicles, with a small electric drivemotor having a motor shaft, with a worm of a worm gear pair, the wormpreferably being made of plastic and slipped onto the motor shaft, witha driver made of a harder material which transfers higher torques thanthe plastic of the worm on the motor shaft, with a worm wheel of theworm gear pair preferably being made of plastic and coupled to the wormvia teeth which engage one another, the driver on a diameter which ismuch greater than that of the motor shaft having a worm form-fit elementand the worm having a driver form-fit element which engages the wormform-fit element of the driver.

2. Description of Related Art

Electric motor-driven servo-drives of this type are being increasinglyused in motor vehicles for a host of applications. One specialapplication is servo-drives on motor vehicle door locks in centrallocking systems (side doors, rear doors, rear hatch). Many otherapplication are known, from the adjustment of headlights throughadjustment of sideview mirrors to headrest and seat height adjustments.Electric motor-driven servo-drives of this type are however also used inmany other technical means.

The starting point for the invention is an electric motor-drivenservo-drive for use in a central locking system of a motor vehicle(published German Patent Application No. 39 32 268), in which a smallelectric drive motor is mounted on a base plate and has a motor shaft onwhich a worm is attached. The worm engages the toothed segment of a wormwheel, the two together form a worm gear pair. In this prior art theworm consists of a metal combination, specifically phosphor bronze,while the worm wheel consists of plastic, especially thermoplastic. Inthis way certain coefficients of friction between the rows of teeth orannular gears which engage one another are achieved.

In the known prior art the electric drive motor is turned off as soon asthe swivel element which is driven via the worm gear pair strikes arubber stop. This so-called blocking mode however entails comparativelyhigh torques to be transmitted during shut-off which can likewisenecessitate making the worm from a metal combination, here from phosphorbronze.

While at the high loads to be expected during operation with respect tothe torque to be transmitted, worms generally made of metal are used andare pressed onto the smooth or notched motor shaft, at the lower loadsto be expected in operation, for reasons of cost, plastic worms are alsowillingly used and in the same way they are pressed onto the smooth ornotched motor shaft or onto the appropriately flattened motor shaftprovided with a corresponding flattened area. This simpler and moreeconomical version of an electric motor-driven servo-drive however for along time has been prohibited where high torques must be transmitted andmainly with frequent occurrence of the aforementioned blocking mode. Iffor example a plastic worm with the corresponding opposite flattenedarea is slipped for example on the flattened motor shaft of a smalldrive motor (the diameter of the motor shaft is roughly 2 mm) thisconnection is generally unable to transmit higher torques over a longertime or the torques which occur in the blocking mode.

In a completely different specialty, specifically the knobs for radiosand other control devices, the problem of overly high Hertzian stressbetween flattened metal and plastic parts has been known for decades(U.S. Pat. No. 3,188,124 from 1963). The problem is generally solvedthere by inserting or pushing a metal reinforcing piece (plate) into theplastic part which is made as a sleeve in the area of the flattening.This prevents occurrence of especially dangerous edge stresses on theedges of the flattened area of the plastic material and routes them intothe metal plate. This technique which has been known for decades incontrol knobs has not had any effect on the area of electricmotor-driven servo-drives with worm gear pairs.

SUMMARY OF THE INVENTION

The teaching of the invention is thus based on the problem of devisingan electric motor-driven servo-drive which economically has a plasticworm, but at the same time can transmit high torques via the worm gearpair and in particular allows permanent blocking operation of theservo-drive.

The aforementioned object is achieved in an electric motor-drivenservo-drive with a small electric drive motor having a motor shaft, witha worm of a worm gear pair, the worm preferably being made of plasticand slipped onto the motor shaft, with a driver made of a hardermaterial which transfers higher torques than the plastic of the worm onthe motor shaft, with a worm wheel of the worm gear pair preferablybeing made of plastic and coupled to the worm via teeth which engage oneanother, the driver on a diameter which is much greater than that of themotor shaft having a worm form-fit element and the worm having a driverform-fit element which engages the worm form-fit element of the driverby a gear form-fit element being provided at at least one location,proceeding especially from the end, by the driver being slipped onto themotor shaft and with the corresponding shaft form-fit element engagingthe gear form-fit element of the motor shaft, the gear and shaftform-fit elements which engage one another being made as flattened areasor flat pieces, and by the worm on the end facing the drive motor havinga slip-on mount for the ring-shaped driver, the driver being made as apunched part of a metal or a metal combination or a metal alloy,especially brass or bronze.

According to in the invention, the plastic worm is combined with adriver of harder material which transmits higher torques, especiallymetal or a metal combination. The high surface pressures (Hertzianstresses) on the form-fitting elements of the motor shaft and the driverwhich engage one another as a result of the small diameter of the motorshaft are reduced to a degree which is feasible for a plastic worm bythe form-fitting elements which engage one another occurring between thedriver and the plastic worm with a much greater diameter and thus withmuch larger force transfer surfaces.

As a result, with an economical, small extra part, specifically thedriver of harder material, especially metal or a metal combination,cost-saving use of a plastic worm can be enabled. This combination ismuch more economical than the use of a worm consisting completely ofmetal, for example phosphor bronze, as in the past.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows in a schematic view one preferred embodiment of an electricmotor-driven servo-drive according to the invention for use in motorvehicles, for example in the central locking system,

FIG. 2 shows a section along A—A in FIG. 1, and

FIG. 3 shows a representation of another embodiment of a electricmotor-driven servo-drive according to the invention which corresponds toFIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a classical arrangement of a electric motor-drivenservo-drive for use in motor vehicles, for example in a motor vehicledoor lock for the function of a central locking system. The teaching ofthe invention is not limited to electrical servo-drives for centrallocking systems, but also relates to electric servo-drives for all typesof functions in motor vehicles. In addition, electric motor-drivenservo-drives according to the teaching of the invention can be found notonly in motor vehicles, but in all technical means where any componentsmust be moved (adjusted) by an electric motor.

The electric motor-driven servo-drive shown in FIG. 1 has, first of all,a support 1 which is only suggested here. A small electric drive motor 2is mounted on the support 1. The motor has a motor shaft 4 which isprovided with a gear form-fit element 3 at at least one location,proceeding especially from the end. A worm 5 of a worm gear pair isslipped onto the motor shaft 4. The worm gear pair furthermore has aworm wheel 6 which is coupled to the worm 5 via teeth which engage oneanother. For small electric motor-driven servo-drives, the worm wheel 6generally consists of plastic. But other materials, for example metal,or composite structures, are also conceivable.

According to the teaching of the invention, the worm 5 consists ofplastic, preferably thermoplastic. As was explained above, theattainable surface pressures (Hertzian stresses) between the plastic andmetal are comparatively small. In order that the plastic worm 5 not weartoo quickly even when transferring high torques and especially in theblocking mode, it is provided according to the invention that a driver 7consisting of a harder material which transfers higher torques than theplastic of the worm 5 is slipped onto the motor shaft 4, and with thecorresponding shaft form-fit element 8 engages the gear form-fit element3 of the motor shaft 4, that the driver 7 on a diameter which is muchgreater than that of the motor shaft 4 has a worm form-fit element 9 andthat the worm 5 for its part has a driver form-fit element 10 whichengages the worm form-fit element 9 of the driver 7. The term “slipped”in this connection means not only loose axial slipping-on, butalternatively also slipping-on with considerable expenditure of forceuntil pressed or shrunk on.

FIG. 2 shows especially well how the teaching is to be understood. Thehighest surface pressures occur on the gear and shaft form-fit elements3, 8 which engage one another. Conversely the torque to be transmittedbetween the worm and driver form-fit elements 9, 10 is distributed overa much larger surface, which as a result of its larger diameter, leadsto much lower surface pressures.

In FIG. 2 in conjunction with FIG. 1, is it apparent that in theembodiment shown here the worm and driver form-fit elements 9, 10 whichengage one another are made as annular gears or sector gears.Conversely, in the embodiment of FIG. 3, it is provided that theseform-fit elements 9, 10 are made as polygons, especially squares(external squares, square sockets).

For the execution of the gear and shaft form-fit elements 3, 8 whichengage one another, FIG. 2 shows the execution as a flattened area orflat piece. Here, alternatives as notched teeth or a polygon or the likecan also be accomplished.

The embodiment shown in FIG. 2 illustrates another measure which isprovided in addition for force transfer from the motor shaft 4 to thedriver 7. It can be recognized that the driver 7 has a radial groove 11into which a driving tang 12, which is connected to the motor shaft 4 orwhich is molded onto it, fits. In this sense connected means connectedby contact of material, therefore, for example, welded. Molded on in onepiece means a corresponding molding process. In any case torque whichacts on a large diameter on the driver 7 can be transmitted via theinteracting driving tang pin 12 and the radial groove 11.

Regardless of the coupling of the driver 7 to the motor shaft 4, it canbe recommended that in addition also the worm 5 has a shaft form-fitelement which engages the gear form-fit element 3 of the motor shaft 4.This shaft element in FIG. 2 would have the same position as the shaftform-fit element on the driver 7, the two form-fit elements would sitonly axially at different locations relative to the motor shaft 4.

It is feasible for bearing in the support 1 that the worm 5 and thedriver 7 are axially movable relative to the motor shaft 4. As a resultof the directions in which the force acts and of the bearing tolerancesthere is always a certain relative displacement between the worm wheel 6and the worm 5 depending on the load direction. So that the drive motor2 can remain stationary, but nevertheless the worm 5 can execute slightaxial relative motion relative to the motor shaft 4, an axialdisplacement capacity which is also known as such from the prior art isrecommended.

FIG. 3 shows one alternative embodiment which is characterized in thatthe driver 7 is made as a cylinder body which is inserted into anaxially running mount 13 which is essentially cylindrical aside from thedriver form-fit element 10 in the worm 5. While in the embodiment shownin FIG. 2 the worm 5 is located radially within the driver 7, theembodiment shown in 10FIG. 3 shows the reversed arrangement with insidedriver 7 and surrounding plastic worm 5.

The embodiment shown in FIG. 2 in conjunction with FIG. 1 shows a driver7 which Ha has small extension in the axial direction. It is providedthat the worm 5 on the end facing the drive motor 2 has a slip-on mount14 for the generally ring-shaped generally driver 7.

For assembly purposes, the driver 7 in the embodiment shown is slippedonto the slip-on mount 14 of the worm 5 from the end facing the drivemotor 2, and thereupon fixed preferably by catching. Fixing can also bedone by simple force fit which however may not be as reliable inoperation. Of course cementing techniques can also be used.

It is critical for the teaching of the invention that the high surfacepressures which are recorded when high torques occur on the motor shaft4 of small diameter arise solely between metal parts, conversely theforce is transferred into the plastic worm 5 over large surfaces andthus with low surface pressures.

In the embodiment from FIG. 2 it can be easily recognized that in thisembodiment it is a good idea to injection-mold the driver 7 in aninjection molding production process with the material of the plasticworm 5. This yields an intimate connection of the materials via thenotched toothing implemented in this example and at the same time goodaxial fixing.

It has already been explained above which materials for the driver 7 areused with consideration of operating stresses. In particular theyinclude metals or metal combinations or metal alloys, especially ofbrass or bronze. The driver 7 can be made as a sintered part, injectionmolded part, punched part, etc.; here, there are many alternativeproduction techniques.

What is claimed is:
 1. Electric motor-driven servo-drive comprising asmall electric drive motor with a motor shaft, a worm of a worm gearpair, the worm being made of plastic and being slid onto the motorshaft, a driver made of a harder material which transfers higher torquesthan the plastic of the worm on the motor shaft, a worm wheel of theworm gear pair, the wheel being made of plastic and being coupled to theworm via teeth which engage one another, the driver having a wormform-fit element of a diameter which is much greater than that of themotor shaft and the worm having a driver form-fit element which engagesthe worm form-fit element of the driver; wherein the motor shaft isprovided with a gear-form fit element at at least one location; whereinthe driver is slid onto the motor shaft and has a corresponding shaftform-fit element which engages the gear form-fit element of the motorshaft; wherein the gear and shaft form-fit elements which engage oneanother have flat areas; wherein the worm has a slip-on mount for thedriver on an end facing the drive motor; wherein the driver is made of amaterial selected from the group consisting of a metal, a metalcombination or a metal alloy; and wherein the driver is a generallyring-shaped punched part.
 2. Servo-drive as claimed in claim 1, whereinthe driver has a radial groove into which a driving tang on the motorshaft fits.
 3. Servo-drive as claimed in claim 2, wherein the worm andthe driver are axially movable relative to the motor shaft. 4.Servo-drive as claimed in claim 2, wherein the driver is fixed on theslip-on mount by catching.
 5. Servo-drive as claimed in claim 1, whereinthe worm and the driver are axially movable relative to the motor shaft.6. Servo-drive as claimed in claim 1, wherein the driver is fixed on theslip-on mount by catching.